As the former mayor of New York, Michael Bloomberg spent an unprecedented three terms grooming one of the greatest cities in the world. Residents can thank him for rolling out 311, their community-action hotline that allows officials to fix and track trends in civic breakdowns. What may be less well known is that as he prepared to leave office a few years ago, Bloomberg created a way to continue that work, albeit indirectly. In 2013, his charitable giving group Bloomberg Philanthropies launched the Mayors Challenge, a $9 million competition in which city leaders dream up their own urban fix-it projects, and then go head-to-head for the right to fund them.

Every year or so, the competition focuses on one region in particular. It started in the U.S., then skipped to Europe and, this year, is open to Latin American and Caribbean cities; 290 cities submitted proposals. A selection committee comprised of 13 regional policy experts reduced that to 20 finalists this week. By year end, one mayor will earn $5 million for his or her cause. Four others will gain $1 million for their own projects. "The idea was to challenge cities to think in big, bold new ways," says James Anderson, the group's head of government innovation. As cities become more inventive and self-reliant, their models may be adaptable elsewhere. As Anderson puts it, "the most powerful change strategy that we can unleash among cities is the spreading of solutions that work."

For the most recent contingent, more than 900 cities were invited to try out. More than 30% of those did—a participation rate record. According to the Bloomberg Philanthropies website, criteria is based on the idea's vision, impact potential, plan of action, and potential to spread.

In July, those finalists will head to "Ideas Camp," a two-day workshop in Bogota, Colombia that’s like a professional development seminar with coaching for how to best propose, pitch, rally support for, and demonstrate the effectiveness of those ideas. Most importantly, mayors are encouraged to collaborate. "It is one thing for a funder to tell you what they like, but it comes across very powerfully and differently when one city tells another what makes sense and what doesn’t," Anderson says. Finalists' refined concepts are due back to the selection committee in September, and winners will be announced toward the end of the year.

One common thread among many of this year’s standouts: How to best care for metropolises' most vulnerable: the elderly, disabled, immigrants, or unemployed teens. Because Latin America is a place with less technology and more distrust of leadership, many plans propose to close those gaps with, job training, citizen-run data collection, or social service programs. In Medellín, Colombia, for instance, a program to battle organized crime would create neighborhood-led lending collectives for low-interest commercial loans and jobs leads. That reduces the need for locals to borrow money illegally. Here’s a full list of proposals.

So what happens to those finalists who go home with nothing? After the European stage, 50% of them continued to hone their ideas. (Bloomberg Philanthropies didn't track U.S. competitors, but now checks in and continues to offer coaching.) Many may feel a moral imperative: It's hard to quit something that could help folks once you’ve established the need.